The Sensitivity of U.S. Surface Ozone Formation to NOx and VOCs as Viewed from Space: the Ozone Monitoring Instrument (OMI)

Bryan Duncan1, Yasuko Yoshida1, Jennifer Olson2,

Sandy Sillman3, Christian Retscher1, Ken Pickering1, Randall Martin4, Ed Celarier1, Jim Crawford2

1NASA Goddard Space Flight Center2NASA Langley Research Center

3University of Michigan4Dalhousie University

October 20, 2009, CMAS meeting, North Carolina

NOx + VOCs → Ozone

Main Ingredient in Smog

OMINO2

OMIHCHO

h

SO2 NO2HCHOCOO3

Ozone has little vertical variation.

Which reactant is the limiting reagent that controls ozone production?

NOx + VOCs → Ozone

OMI HCHO/NO2: Air Quality Indicator*

• If HCHO/NO2 is low then one must reduce anthropogenic VOCs to lower ozone.

• If HCHO/NO2 is high then one must reduce NOx to lower ozone.

hv

NOTE: HCHO/NO2 gives info on the sensitivity of instantaneous ozone production, not the ozone concentration!

*Based on Sillman [1995]Martin et al. [2004]

OMI HCHO/NO2 : August 2006

VOC controls O3 prod. NOx controls O3 production

Lots of Isoprene =NOx controls

Low VOCs =VOC controls

Transition is “fuzzy”: ~1.2-2.2!

NOx – limited regimeVOC – limited regime

VOC controls O3 prod. NOx controls O3 production

OMI HCHO/NO2 : August 2006

Southwest US Northeast US

LA

SanFrancisco

Las Vegas

CentralValley

Toronto

DCPhilly

NYC

Richmond

Boston

Phoenix

OMI captures gradient from downtown to suburbs to rural areas!

Min Ratio Max Ratio

Minimum & Maximum Ratios of 9 Summer Months

The ratio is increasing as NOx emissions decrease. Therefore, ozone formation is becoming more NOx-limited.

Variability Associated with NOx Emissions

June-August OMI NO2: 2007-2005

Wildfires in2007

Point sources 10% lower in 2007 due to NOx Budget Trading Program of EPA.

Automobile emissions decreased due to Tier 2 Vehicle and Gasoline Sulfur Program.

Variability Associated with Isoprene

Therefore, ozone formation should be more NOx-limited during high ozone events.

But, NOx emissions decreasing!

Isoprene emissions and, subsequently, HCHO increase with temperature.

Therefore, HCHO/NO2 should increase with temperature.

We know that high O3 events increase with temperature.

Conclusions

The OMI ratio appears to be a credible air quality indicator and is consistent with in situ observations.

Ozone production became more NOx-limited over the U.S. from 2005-2007 because of substantial NOx emission reductions.

Ozone production should be more NOx-limited during heat waves in regions with high biogenic emissions.

The fine horizontal resolution allows us to see the gradient in the ratio from urban to suburban to rural areas.

Currently analyzing CMAQ output. Stay tuned!

Extra Slides

CMAQ Tropospheric Column : HCHO/NO2

4x4 km2 horizontal resolution

July 1st – 4th mean in 2007 at 1-2 pm

Provided by Yongtao Hu, Georgia Tech

Instantaneous Ozone Production Rate (x107 molec/cm3-s) vs HCHO/NO2

Transition: HCHO/NO2 ~1.2-2.2

Transition: HCHO/NO2 1.4-2.6

(for NO2 columns > 2.5x1015 molec/cm2)

Assume Transition= 1

NASA Langley box model output. (Provided by Jennifer Olson)

CMAQ

CMAQ

CMAQ 4 km2 horizontal resolutionover Southern California. (Provided by Yongtao Hu, Georgia Tech)

How do tropospheric and PBL columns (x1015 molec/cm2) compare?

1:1

How does the Instantaneous O3 Production Rate vary with the PBL column (x1015 molec/cm2), [HCHO], and [NO2]?

CMAQ 4 km2 horizontal resolutionover Southern California. (Provided by Yongtao Hu, Georgia Tech)

NASA Langley box model output. (Provided by Jennifer Olson)

OMI HCHO as Proxy for Variability of Isoprene Emissions

Above Normal Rainfall

Serious Drought

Historic Drought

Major player in AQ! ~22% Variation